Cyclohexene carboxylic acid esters and process for preparing same



Patented Aug. 7, 1951 UNITED STATES PATENT OFFICE 2,583.2 GYGLO CARBOXYLIC ACID ESTEBS AND PROCESS FOR PREPARING SAME Ernst Bcrgmann, London, England, assignor to Polymerlsahlc Products Limited, London County, England, a British company No Drawing. Applicationnecember 23,1946, Serial No. 718,110 11 claims. (Cl- 260-468) 2 It has been known since the fundamental work of Diels and Alder that dienes, such as butadiene or isoprene condense with unsaturated acids and their derivatives such as esters or nitriles to form hydroaromatic systems of the general formula If the philodienic component (the reactant which combines with butadiene or isoprene) belongs to the very simplest aliphatic unsaturated substances such as derivatives of acrylic or methacrylic acid, high molecular rubber-like condensation products are formed.

The present invention covers a process for the production of the simple hydroaromatic condensation products from butadiene or isoprene with the derivatives of acrylic or methacrylic acid, in such a manner that the formation of polymeric products (high polymers) is suppressed.

The invention thus includes a process which consists more specifically in the synthesis of the nitrile of 3-cyclohexene-carboxylic acid CN and the nitrile of 1-methyl-3 cyclohexene-carboxylic acid and the esters of these acids, and similar derivatives, by condensation of butadiene or isoprene, respectively, with the nitriles or esters of acrylic o'r methacrylic acid.

The present invention also includes the preparation of the nitrile of teh'a-hydro-benzoic acid and similar bodies (without polymerizing the same) by the aforesaid components in the presence of a polymerisation inhibitor of the group consisting of phenols and polyphenols, their alkyl derivatives and tannic acid and trinitrobenzene.

If butadiene, e. g. and acrylonitrile are heated to a temperature of mil-180 C. in a closed vessel in presence of an inhibitor of polymerization such as hydroquinone or tert. butyl-catechol, and the product of the reaction is fractionated, good yields of the nitrile of tetra-hydro-benzoic acid are obtained. Whilst the formation of high-polymer products is prevented by the addition of the polymerisation inhibitor, the purely thermal homogeneous dimerisation of butadiene to vinylcyclohexene is unaflected by such additive agents, and indeed, certain quantities of this hydrocarbon will be present in the reaction product and can be separated by the fractional distillation. However, it is possible to reduce the formation of this dimeride to a minimum by using the acrylonitrile in an excess, so that its reaction with butadiene occurs at a greater speed than the reaction (condensation) of one butadiene molecule with another.

The present invention includes, therefore, a process according to which butadiene or isoprene are heated together with a substantial excess of the nitrile or an ester of acrylic or methacrylic acid, in the presence of a polymerisation inhibitor of the aforementioned group, at a temperature of 100-180" in a closed vessel for a suitable period 'of time, followed by the isolation of the desired reaction product by fractional distillation.

Butadiene can be condensed not only with acrylonitrile but also with the nitrile of methacrylic acid or with esters of acrylic acid or methacrylic acid such as the methyl or the 2-ethyl-hexyl ester or numerous others. The products so obtained are liquids, sometimes exhibiting pleasant odors, which contain one double bond which lends itself easily to hydrogenation to give the corresponding cyclohexane derivatives.

The nitrile and the ester groups can be hydrolysed in the conventional manner and the corresponding acids thus become easily available. The cyclohexene derivatives are capable of the normal reactions of acids of that structure, e. g. esteriflcation with monoand polyvalent alcohols. In this way, the diester of 3-cyclohexene-carboxylic acid with ethylene glycol, having the formula co co b-CHr-CHrJ) CHC\ cm :11, i cm-cn H cn.

ascaaoo 3 the (secondary) monoesters of i-methyi-S-cyclohoxene-carboxyiic acidwith that wool O O cm KO CE: in. rem-ct H C I andwithtrimethyil l 00 o-cm-om-on and Theseacidscanalsohedebydroeenatedtogive benzene derivativu and oxidised with ring fission to carbon-derivatives of adipic acid or substituted adipic mm.

Imples A [Anpartabymitlotildieatedotherwise] Example 1.--79.5 parts acrylonitrile and 100 parts butadiene and parts hydroquinone were heated at 120' for 4 hours. Distillation or that reaction product wave:

(a) 3.5 parts acrylonitriie.

(b) 5 park 180-150. vimi-crciohexene (litera ture:B. P. 138'/700mm.)

(c)l25partsoithedesirednitri1e,B.P.

' Found: C, 66.5; H, 8.8.

Example Z.-Derivatives oi 3-cyclohexene-carboxylic acid, esteriiication. 51 parts of the acid, 64 parts methyl alcohol and 3.0 parts concentrated sulphuric acid were boiled ior 6 hours under reflux. The excess oi methanol was distilled oil and the residue treated with sodium carbonate solution and dried over calcium chloride.

Methyl 3-cyclohexene-carboxyiate boiled at 4 1187100 mm.; yield, 46 parts. Density 1.0108: refractive index, 1.4002.

Anaheim-Cale. tor C-HuOs: C, 00.0; H, 8.0. mm: C, 67.5; H, 8.0.

To25.5partsottheaoidinpartsbyvolume chloroform, 71.4 parts thionyl mentwithdiiutesulturieacidandetheraavean oil.whichdistil1edunder0mm.nressureat155- 160' and was the desired di-ester.

cO-O-Cm-QHr-O Yield, 21 parts=73%; duty, 1.0812; refractive index, 1.4854.

The product would apparentb be HI-C1 0 Analysis.Caic. for Cum: 0, 08.1; H, 9.2. Found: C, 07.5; 07.9; 3.9.2; 0.9.

11.5 parts 3.5-dimethyl-hexane-23-diol in parts pyridine were added to 22.5 parts or the chloride of 2-oyc acid in 37 partschlorolorm. Ai'ter24hom-satroomtemperatm'athemasswastreatedwithdiiuteflasoi, washed with sodium carbonate solution and the. chloroform distilled on. B. P. or the monoester. iractive index, 1.4741.

Anaheim-Cale. for CM: C, 70.9; H, 10.2. Found: C, 09.9; H, 10.0.

Example 3.-Butadiene and methyl methacrylate. 100 parts methyl methacrylate (1 mol), parts butadiene (1.4 moi) and hydroquinone were heated at 150 for 5 hours. The product was twice fractionated at mm. pressure.

(a) 45-60: 24 parts; methyl methacrylate (b) 6647": 1'7 parts; containing vinyl-cyclohexene (0) 116-117": 112 Darts; density 0.9866; refractive index, 1.45815 Analysis-Cale. for CsHuOIt C, 70.1; H, 9.1. Found: C, 70.3; H, 10.1.

Yield, 73% or, calculated on the methyl methacrylate actually consumed, about quantitative. Product (0) is methyl l-methyl-Ii-cyclohexenecarboxylate.

Example 4.-Butadiene and (Z-ethyi-hexyl) methacrylate. 120 parts or the ester and 00 parts butadiene were heated with 10 parts tert. butyl-catechol as inhibitor at 120 for 8% hours and the product was fractionated under 5 mm.. pressure. The following fractions were secured:

(a) 69 parts octyl methacrylate (b) 10 parts 100-125. intermediate cut (0) 26.8 parts -126"; density 0.9245; refractive index 1.4528.

The (2-ethy1-hexyl) l-methyl-Zi-cyclohexenecarboxylate was obtained in 43% yield (calcuaocaaoo bromine No. 75.5. Found: C, 76.2; H, 11.5; bromine No. 60.

Example 5.-1-methyl-8-cyclohexene-carboxylic' acid and derivatives.

(a) 158.4 parts of the methyl ester were stirred with 100 parts potassium hydroxide in 80 parts methyl alcohol and 100 parts water. After 30 minutes of exothermic reaction, a clear soluion had formed, which was boiled for 5 hours and acidified. The solid was freed from adhering potassium sulfate by washing with water (in which the acid is only sparingly soluble), dried and triturated with cold petroleum ether. Yield, 122 parts=86%; M. P. 77-79.

(b) 21 parts of the 2-ethyl-hexyl ester were heated for 8 hours with a solution of 9 parts potassium hydroxide in 80 parts methanol. The product was steam-distilled, and from the distillate 9.6 parts 2-ethyl-hexanol were isolated (yield, 91%). The alkaline residue was acidified and the acid dried and recrystallised from ligroin. Prisms, M. P. 7779; yield 12 parts=quantitative.

Analysis-Cale. for CaHmOz: C, 68.6; H, 8.6. Found: C, 69.0; H, 9.2.

Acid chloride.-To 28 parts of the acid in 25 parts by volume chloroform, 71.4 parts thionyl chloride were slowly added. The sluggishreaction was completed by boiling for 2 hours. Distillation gave 22 parts, boiling at 100/30 mm.

parts 3.5-dimethyl-hexane-2.3-diol in 50' parts pyridine were added to a solution of 22 parts of 1-methyl-3-cyclohexenoyl chloride in parts by volume chloroform. The usual treatment gave 12.5 parts of the monoester, B. P. 125-l30/6 mm.; density, 1.0274; refractive index, 1.4669.

22 parts trimethyl glycol, 62 parts methyl 1-methyl-3-cyclohexeneoate and 2 parts sodium methoxide were heated in a column in a bath of 130 C. Within 8 hours, 4 parts methanol collected in the receiver. The mass was treated with dilute sulfuric acid and the product distilled repeatedly under 5 mm. :pressure. 20.5 parts of the methyl ester were recovered unchanged. The desired mono-(1-methy1-3-cyclohexenoyl) -derivative of trimethyl-glycol had B. P. 105-ll0/4 mm.; density, 1.0223; refractive index, 1.4690.

Analysis-2110. for C13H22O3: C, 69.0; H, 9.7; bromine number, 71. Found:' C, 69.0; H, 9.6; bromine number, 79.

6.2 parts ethylene glycol, 31 parts methyl 1-methyl-3-cyclohexeneoate and 2 parts sodium methoxide were heated at 130 bath temperature in a column. Within 4 hours, 5.6 parts methanol collected in the receiver. Treatment as above gave two fractions:

(a) 185-15575 mm.; 7.5 parts; mono-ester; density, 1.0614; refractive index, 1.4770

(b) 160170/5 mm.; 10 parts; di-ester; density,

1.0648; refractive index, 1.4844.

Analysis-Cale. for C10H16O32 C, 65.2; H, 9.2; bromine number, 105; OH,9.3. Ciel-12504: C, 70.6; H, 8.5; bromine number, 105; OH, 0. Found (a): C, 64.4; H, 8.7; bromine number, 90; OH, 7.4. (b): C, 70.5; H, 8.7.

The Z-aIkyI-butadienes, isoprene and its homologs, will give mostly derivatives with the alkyl-group in para position, but as by-products, meta-compounds are formed. The operating conditions are the same for all these dienes.

If desired, instead of the 100 parts of butadiene in Example 1, 120 parts of isoprene can be used. The product thus formed is mainly the nitrile of 4-methyl-3-cyclohexene-carboxylic acid, but it 6 contains usually certain amounts of the ,8- methyl-compound. Dehydrogenation of'this liquid product w ich boils at 68-69/6 mm, leads to a mixture 0 mand p-tolunitrile which can be separated from each other.

I claim: 1. A process of producing a product of the type in which X represents a substance selected from the group consisting of hydrogen and methyl and in which Y represents a monovalent radical selected from the group consisting of COO-alkyl and CN, which comprises heating a mixture consisting essentially of a diene containing 4 to 5 carbon atoms and an excess of a derivative of an unsaturated organic acid, selected from the group consisting of the nitriles and alkyl esters of acrylic acid and methacrylic acid, whi1e in the presence of a polymerization inhibitor selected from the group consisting of phenols and polyphenols and their alkyl derivatives, tannic acid and trinitrobenzene, until a condensation of such two main components is effected.

2. A process of making an unpolymerized product of the type in which X represents a substance selected from the group hydrogen and methyl and in which Y represents a monovalent radical selected from the group consisting of COO-alkyl and -CN, which comprises heating at between and C., a

mixture consisting essentially of 1 mol of a sub- COOH in which X is a substance selected from the group consisting of hydrogen and a methyl group such ester being in a substantially unpolymerized condition, and being non-resinous in character.

4. A monomeric polyhydric alcohol ester of methyl-cyclohexene-carboxylic acid.

5. A monomeric glycol ester of cyclohexenecarboxylic-acid.

6. A monomeric glycol ester of methyl-cyclohexene-carboxylic acid.

7. A monomeric ester of cyclohexene-carboxylic acid with a glycol, said ester still containing one of the OH groups of the glycol, unesterified.

8. A monomeric ester of monomethyl-cyclohexene-carboxylic acid with a glycol, said ester still containing an OH group of the glycol, un-

75 esterifled.

I. A monomeric ester or B-oyclohexene carboxyllc sold with 3.5 dlolkyl hexane-2.34101.

10. A monomerlc ester of 1-methyl-3-cyclohexene-cni'boxyllc mold wlth I zlycol selected from the group consisting of ethylene zlyeol, 3.5-dlmethyl-hexane-ZQ-dlol and trlmethyl glycol.

' 11. A mono-(l-metbyl-3-cy'clohexenoyl) es ol'trlmethyl-zlycol.

ERNST BERGMANN.

some 8 UNITED STAT" PAW Number Name I Date 1,824,068 Brooks Sept. 22, 1931 2,017,070 num- Oct. 10, 1935 2,217,682 Wolfe Oct. 8, 1940 2,409,688 Kropa Oct. 22, 1946 FOREIGN PATENTS v Numb" Country I). 540,168 Great Britain Oct. 8, 1041 ammonia Thetollowlncmereneumotreeordmthe meotthlspotent:

OTHER cm Ber. No. 415,424. Hop! et :1, (A. P. 0.), publllhed Aprll 20, 1943. 

1. A PROCESS FOR PRODUCING A PRODUCT OF THE TYPE
 3. A POLYHYDRIC ALCOHOL ESTER OF AN ACID HAVING THE GENERAL FORMULA 